In studies of cognitive performance in aged rhesus monkeys, recognition memory was assessed in eight rhesus monkeys of advanced age (25 to 27 years of age) using the delayed recognition span test (DRST), and their performance was compared to that of five young adult animals (5 to 7 years of age). The DRST is a task that requires the monkey to identify a novel stimulus from an increasing array of familiar stimuli and, thus, provides a measure of performance in response to increasing memory load. DRST performance was tested on two stimulus conditions (spatial position and color), and both trial-unique and repeating series were employed for each of the two conditions. As a group, aged monkeys were impaired on both the spatial and color conditions of the DRST, achieving about two-thirds of the span of the young adult group in each condition. Error analyses revealed that monkeys in the aged group also produced more preservative responses (i.e., displacing the previously corre ct disk) than did young adults. The findings suggest that monkeys of advanced age are impaired on tasks with memory loading demand characteristics.